1. Field
The field is pad printing, and in particular rotary transfer pad printing.
2. Prior Art
Fixed Pad Printing
Prior-art, fixed-pad printing is used to apply images and text to either flat or uneven surfaces ranging from poker chips and golf balls to household appliance panels. Such printing usually employs a domed pad. The pad is made of an elastomeric material such as gelatin or a silicone rubber. The surface of a flat, metal or plastic plate is etched to a depth of about 0.025 mm with an image. The etched plate is called a cliché. The pad is pressed against the cliché, flattening the domed portion and contacting the ink in the image. The pad is then lifted away from the cliché, carrying the ink image with it. The pad is then moved to a position in proximity with a receiving surface. The pad is then pressed against the receiving surface, again deforming its domed shape, until all image areas are in contact with the receiving surface. The pad is then lifted away from the receiving surface, leaving behind the ink image on the surface. This completes the transfer of the image from the cliché to the receiving surface.
The pad is domed to prevent the entrapment of air during the inking and transfer steps. Air entrapped during these operations would form pockets which would be undesirable since such pockets could release their contents in unpredictable ways, causing the ink image to smear across the surface of the cliché or the receiving surface.
Pad printing is most useful when the surface to be printed is uneven, i.e., wavy or contoured. The pad can carry the ink image to all points on the receiving surface since it is deformable and thus can conform to such points.
Pad Printing
Our U.S. Pat. No. 6,840,167 (2005) teaches a multicolor and multi-layer apparatus for pad printing using a deformable pad. This apparatus is generally limited to printing images that are the same size or smaller than the pad itself.
Rotary Pad Printing
In the past, rotary pad printing has been used to decorate objects by printing images or text thereon. In its simplest form, a rotary pad printing apparatus comprises a rotary pad that comprises a multi-layer, right-circular cylinder having a compressible surface that is usually made of silicone rubber. The cylinder is first inked using a cliché and then brought into rolling contact with a receiving surface such as a bottle or a syringe. This method of pad printing is best used with monochrome images that are applied over a limited area.
Co-Pending Application
In our above co-pending application Ser. No. 11/777,166, we teach a method and apparatus for rotary pad printing that overcomes many of the prior-art limitations. Although this system provides a significant improvement in pad printing technology, there remains at least one area for improvement. In the prior-art rotary pad printing systems, the surface of the pad remains flat in its axial direction. I.e., the rotary pad assembly comprises a right-circular cylinder. In another aspect of the embodiment, the rotary pad is replaced by a belt. The belt offers the same opportunity for improvement.
Rotary Pad Printing Apparatus—FIGS. 1 and 2
A prior art rotary pad printing wheel, as shown in FIGS. 1A and 1B, comprises a silicone rubber cylinder 100 having an outer surface 101 and formed around a metal shaft 105. In use, ink is applied image-wise to surface 101 at a known inking station (not shown), and then subsequently transferred to a receiving surface (not shown) as the pad rotates in contact with the receiving surface.
Similarly, a prior art rotary belt, taught in our above co-pending application Ser. No. 11/777,166 and indicated in FIGS. 2A and 2B, comprises a silicone rubber belt 200 having a surface 215, and rollers 205 and 210. One or both of rollers 205 and 210 propel and support belt 200. An inking station (not shown) applies an ink image to surface 215 of belt 200 at one location, and the ink is subsequently applied to a receiving surface (not shown) as belt 200 traverses its path and comes into contact with the receiving surface.
In both of the above-described cases, the receiving surface and the surface of the pad or belt are stationary with respect to one-another during transfer to avoid smearing of the ink image. This apparatus is best suited to printing cylindrical surfaces whose axis is either parallel to or perpendicular to the axis of rotation of the pad wheel or belt.